Rewrite as a simplified fraction. ${2.1\overline{50} = {?}}$
Explanation: Let $x$ equal the decimal. Set up two equations such that the digits after the decimal point are identical. ${\begin{align*}1000x &= 2150.505...\\ 10x &= 21.505...\end{align*}}$ Subtracting the two equations, we have: ${990x = 2129}$ ${x = \dfrac{2129}{990}} \text{or} {2 \dfrac{149}{990}}$